CN115401175A - Method for producing large-size high-carbon chromium bearing steel bar with small compression ratio - Google Patents
Method for producing large-size high-carbon chromium bearing steel bar with small compression ratio Download PDFInfo
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- CN115401175A CN115401175A CN202210854647.5A CN202210854647A CN115401175A CN 115401175 A CN115401175 A CN 115401175A CN 202210854647 A CN202210854647 A CN 202210854647A CN 115401175 A CN115401175 A CN 115401175A
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/10—Supplying or treating molten metal
- B22D11/11—Treating the molten metal
- B22D11/114—Treating the molten metal by using agitating or vibrating means
- B22D11/115—Treating the molten metal by using agitating or vibrating means by using magnetic fields
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
- B21B1/16—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling wire rods, bars, merchant bars, rounds wire or material of like small cross-section
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B37/00—Control devices or methods specially adapted for metal-rolling mills or the work produced thereby
- B21B37/46—Roll speed or drive motor control
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/12—Accessories for subsequent treating or working cast stock in situ
- B22D11/1206—Accessories for subsequent treating or working cast stock in situ for plastic shaping of strands
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/16—Controlling or regulating processes or operations
- B22D11/18—Controlling or regulating processes or operations for pouring
- B22D11/181—Controlling or regulating processes or operations for pouring responsive to molten metal level or slag level
- B22D11/182—Controlling or regulating processes or operations for pouring responsive to molten metal level or slag level by measuring temperature
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/16—Controlling or regulating processes or operations
- B22D11/20—Controlling or regulating processes or operations for removing cast stock
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/16—Controlling or regulating processes or operations
- B22D11/22—Controlling or regulating processes or operations for cooling cast stock or mould
- B22D11/225—Controlling or regulating processes or operations for cooling cast stock or mould for secondary cooling
Abstract
The invention discloses a method for producing a large-size high-carbon chromium bearing steel bar with a small compression ratio, which comprises the following steps of continuous casting and continuous rolling, wherein the continuous casting step comprises the following steps: protecting and pouring in the whole process, wherein the temperature of molten steel in the tundish is 1465-1485 ℃; the electromagnetic stirring current of the crystallizer is 330-350A, and the frequency is 3-4 Hz; the current of two cold end electromagnetic stirring is 340-360A, the frequency is 8E9Hz; the withdrawal speed of the continuous casting billet is 0.8-1.0 m/min, and the secondary cooling solidification is carried out, wherein the secondary cooling strength is 0.2-0.3L/kg; the central porosity of the obtained continuous casting square billet is not more than 2.0 grade, the central shrinkage cavity is not more than 1.5 grade, and the section size is 197-205 multiplied by 197-205 mm 2 (ii) a The continuous rolling process comprises the following steps: putting the continuous casting square billet into a steel rolling heating furnace for heating; after the continuous casting billet is discharged, the continuous casting billet enters a roughing mill, and the outlet speed of a finished product with the diameter of 70-90 mm of the round steel is 0.90-1.5 m/s; rolling into round steel with the diameter of 70-90 mm. The method adopts a small compression ratio to produce large-sized bars, enlarges the production capacity of equipment and improves the utilization rate of the existing process equipment.
Description
Technical Field
The invention relates to a manufacturing technology of alloy steel in the metallurgical industry, in particular to a method for producing a large-specification high-carbon chromium bearing steel bar with a small compression ratio.
Background
High carbon chromium bearing steel has been produced by continuous casting technology in the early 80 s abroad. Domestic special steel enterprises began to research the smelting and continuous casting technology of high-carbon chromium bearing steel in the 90 s. Because related process equipment is incomplete in matching and the problems of center segregation and center porosity are easily caused, domestic and foreign special steel enterprises generally adopt a one-fire or two-fire continuous casting-rolling production method of bloom continuous casting billets, and the internal quality of the material is improved by utilizing a larger metal compression ratio.
In recent years, the metallurgical industry has vigorously developed continuous casting process technology to continuously reduce the total compression ratio of hot continuous rolled bars. However, for the continuous casting process, it is essential to minimize the center porosity and center segregation as much as possible to ensure high quality of the slab. Under the condition of ensuring the quality of the continuous casting billet, the finished steel product can meet the corresponding performance requirement only by rolling through a certain compression ratio. In the state of the art of continuous casting, the strand dimensions are still not infinitely close to those of the finished product, in particular of alloy steel continuous casting billets, and the necessary reduction ratios must be taken into account in view of the compactness of the strand.
The high-carbon chromium bearing steel GCr15 belongs to hypereutectoid steel, the carbon content is up to 1 percent, so that the temperature difference between the liquidus and solidus of molten steel is relatively large, and the shrinkage in the solidification and cooling process is larger than that of common low-carbon steel. The GCr15 casting blank shrinks in volume in the solidification process and transfers heat outwards to ensure that the volume shrinkage generated by continuously cooling the solidified part in the center of the casting blank cannot be supplemented by molten steel, so that periodic and intermittent shrinkage cavities are generated in the center of the casting blank. The central shrinkage cavity of the continuous casting billet can not be healed in the rolling process, so that the shrinkage cavity exists on the round steel, and the performance of the steel is seriously influenced. From the literature, the reduction ratio (the ratio of the cross-sectional area of the billet to the cross-sectional area of the steel) of the billet rolled steel in the continuous casting of the high-carbon chromium bearing steel is normally about 20, preferably about 15, and the domestic reduction ratio is at least 14.
For bars produced by rolling, the rolling compression ratio is a key process parameter for determining the texture performance of a rolled piece, and the compression ratio is expressed by the ratio of the cross sectional area of the rolled piece before rolling to the cross sectional area of the rolled piece after rolling. In the past, it was generally accepted that the quality of continuously cast steel products is highly demanding and difficult to control and guarantee, and the quality of the products is often controlled by the size of the compression ratio. The larger the compression ratio, the larger the deformation degree of the blank; if the compression ratio is small, it means that the degree of deformation of the cast slab is small; especially, when a large-section casting blank is rolled, rolling deformation is basically on the surface and subsurface of the large-section casting blank, and the deformation is difficult to permeate into the core, so that the core structure of a finally obtained rolled piece is difficult to improve, metallurgical defects such as porosity and the like are difficult to compact and weld, and further, the mechanical property of a bar product is difficult to stabilize. Therefore, from the viewpoint of improving the properties of the steel product, the larger the compression ratio, the better.
Furthermore, s. enclond, a semi-empirical company distinguished by its research and experimental data, indicates that the rate of deformation of the rolling process has a certain effect on the quality of the inside of the rolled stock. However, for calculating the mean pressure for hot rolling, the formula has a certain range of applicability: the rolling temperature of the billet is more than or equal to 800 ℃, the material is carbon steel (Mn is less than or equal to 1 percent, cr is less than or equal to 2-3 percent), the rolling speed is not more than 20m/s and the like; the formula is shown in formula (1):
in formula (1):
c is (0.9682 + 0.00656v), and the speed range can reach 5-60 m/s after correction;
r is the radius mm of a rolling groove of the roller;
v is the rolling linear speed m/s;
H. h, the thickness of the rolled piece before and after rolling;
B. h is the front and back width of the rolled piece;
Δ H = H-H is the absolute reduction.
The empirical formula for calculating K and eta is shown as formula (2) and formula (3):
K=9.8×(14-0.01t)(1.4+C+Mn) MPa （2）
η=0.1×(14-0.01t) MPa·S （3）
in formulae (2) and (3): t-rolling temperature, DEG C; c-carbon content in%; mn-manganese content in%.
μ is calculated by the following equation (4):
μ= a(1.05-0.0005t) （4）
in formula (4): for steel roll a =1, cast iron roll a =0.8; t is the rolling temperature.
When the temperature t is more than or equal to 800 ℃ and the manganese content is 1.0 percent, the average pressure is in direct proportion to the viscosity coefficient and the average deformation speed; the viscosity coefficient is related to the rolling speed, and the larger the rolling speed is, the smaller the viscosity coefficient is, so the smaller the average unit pressure is. From the above analysis, it can be seen that the average unit pressure increases with a decrease in rolling speed.
Related patent applications relating to the control of the compression ratio of continuous cast high carbon chromium bearing steels are now described below.
The Chinese patent application with the application number CN200410089358.2 provides a production method for reducing and refining D-type inclusions in high-carbon chromium bearing steel; although the document mentions a reduction ratio of > 10, no control method is mentioned in connection with rolling.
Chinese patent application with application number CN200710046394.4 adopts 220X 220mm 2 Rolling 20-75 mm (including 70 mm) continuous casting bearing steel round steel by using the continuous casting billet, wherein the minimum compression ratio is 10.96; in the production process of continuous casting billets, the superheat degree of molten steel in a tundish is controlled to be 20-30 ℃, and the continuous casting drawing speed is controlled to be 0.70-1.10 m/min; the secondary cooling strength is controlled to be 0.30-0.50L/kg, the heating maximum temperature is 1220-1250 ℃, and the total heating time is more than 270 min; but no reference is made to the process parameters of the rolling process.
The Chinese patent application with application number CN02112241.5 adopts a continuous casting bearing steel small square billet (120 multiplied by 120 mm) 2 、140×140mm 2 、160×160mm 2 ) The rolling is performed under the specification of 50mm, and the compression ratio is minimum 9.98. The method mainly explains the control of the steelmaking process, the superheat degree is 20-40 ℃, the pulling speed is 1.9-2.5 m/min, the specific water amount is 0.5-0.9L/kg, and the low-power quality of a casting blank is controlled by matching with electromagnetic stirring, so that the quality of a bearing steel finished product under a small compression ratio is met; but no reference is made to the process parameters of the rolling process.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a method for producing a large-size high-carbon chromium bearing steel bar material with a small compression ratio so as to ensure that the macrostructure of the bar material meets the standard requirement of GB/T18254-2016 high-carbon chromium bearing steel high-quality steel.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows: the method comprises the following steps of continuous casting and bar rolling, wherein the continuous casting process comprises the following steps: protecting and pouring in the whole process, wherein the temperature of the molten steel in the tundish is 1465-1485 ℃; the electromagnetic stirring current of the crystallizer is 330-350A, and the frequency is3-4 Hz; the current of the secondary cooling end electromagnetic stirring is 340-360A, and the frequency is 8-9 Hz; the blank drawing speed of the continuous casting blank is 0.8-1.0 m/min, and the secondary cooling solidification is carried out, wherein the secondary cooling strength is 0.2-0.3L/kg; the central porosity of the obtained continuous casting square billet is not more than 2.0 grade, the central shrinkage cavity is not more than 1.5 grade, and the section size is 197-205 multiplied by 197-205 mm 2 ；
The bar rolling process comprises the following steps: putting the continuous casting square billet into a steel rolling heating furnace for heating; after the continuous casting billet is discharged from the furnace, the continuous casting billet enters a roughing mill, and the outlet speed of the finished product with the diameter of 70-90 mm of the round steel is 0.90-1.5 m/s; rolling into round steel with the diameter of 70-90 mm.
In the bar rolling process, the highest temperature of furnace gas is controlled to be 1200-1250 ℃ during heating, and the total heating time is not less than 240min.
In the bar rolling process, the rolling reduction of the first three roughing mills is respectively 37-45 mm, 53-61 mm and 75-83 mm.
The high-carbon chromium bearing steel is GCr15.
Adopt the produced beneficial effect of above-mentioned technical scheme to lie in: the invention produces continuous casting square billet with central porosity not more than 2.5 grade and central shrinkage cavity not more than 2.0 grade by controlling the superheat degree of molten steel in a tundish, the continuous casting steel drawing speed and the secondary cooling strength and matching with the electromagnetic stirring of a crystallizer and auxiliary equipment of electromagnetic stirring at the tail end, and the section size is 197-205 multiplied by 197-205 mm 2 (ii) a When the bar is rolled, round steel with the diameter of 70-90 mm is produced by reducing the speed of a rolled finished product, and the compression ratio is 6.29-10.40; finally, rolling a large-specification bearing steel bar material by continuously casting a square billet at a small compression ratio, wherein the macrostructure meets the standard requirement of high-quality steel of GB/T18254-2016 high-carbon chromium bearing steel. On the premise of ensuring that the bearing steel performance is qualified, the invention adopts a small compression ratio to produce large-sized bars, thereby enlarging the production capacity of equipment; the invention improves the productivity of a continuous casting machine-steel rolling production line and improves the utilization rate of the prior process equipment; the continuous casting bearing steel round steel with larger specification can be produced by adopting a small-blank continuous casting blank, and the difficulty of the compression ratio control of the existing continuous casting high-carbon chromium bearing steel is broken through.
Drawings
The invention is described in further detail below with reference to the drawings and the detailed description.
FIG. 1 is a macrostructure diagram of a round bar obtained in example 1 of the present invention;
FIG. 2 is a macroscopic view of the round steel obtained in example 2 of the present invention;
FIG. 3 is a macrostructure diagram of a round bar obtained in example 3 of the present invention;
FIG. 4 is a macroscopic view of the round steel obtained in example 4 of the present invention;
FIG. 5 is a macroscopic view of the round bar obtained in example 5 of the present invention.
Detailed Description
The method for producing the large-size high-carbon chromium bearing steel bar with the small compression ratio adopts the processes of converter primary smelting, LF refining, RH vacuum treatment, continuous casting and continuous rolling; the process comprises the following steps:
(1) Primary smelting in a converter, LF refining and RH vacuum treatment: the method comprises the following steps of (1) taking blast furnace molten iron and scrap steel as raw materials, carrying out deoxidation alloying on molten steel through converter primary smelting, carrying out deep deoxidation and degassing to remove impurities through LF refining and RH vacuum treatment, and finally enabling chemical components of the molten steel to meet requirements and controlling the temperature of the molten steel discharged from RH to be 1500-1510 ℃; the GCr15 molten steel comprises the following chemical components in percentage by weight: 0.95 to 1.05 percent of C, 0.15 to 0.35 percent of Si, 0.25 to 0.45 percent of Mn, less than or equal to 0.020 percent of S, less than or equal to 0.020 percent of P, 1.40 to 1.65 percent of Cr, less than or equal to 0.0050 percent of Al, less than or equal to 0.0030 percent of Ti, less than or equal to 0.0010 percent of Ca, less than or equal to 0.10 percent of Cu, less than or equal to 0.10 percent of Mo, less than or equal to 0.10 percent of Ni, less than or equal to 0.04 percent of As, less than or equal to 0.002 percent of Pb, less than or equal to 0.075 percent of As + Sn + Sb, less than or equal to 0.0012 percent of O, and the balance of Fe and inevitable impurities.
(2) Continuous casting: the whole continuous casting process protects the casting, and the temperature of the molten steel in the tundish is 1465-1485 ℃; the electromagnetic stirring current of the crystallizer is 330-350A, and the frequency is 3-4 Hz; the current of the secondary cooling tail end electromagnetic stirring is 340-360A, and the frequency is 8-9 Hz; the continuous casting billet is solidified by secondary cooling at the withdrawal speed of 0.8-1.0 m/min, and the strength of the secondary cooling, namely the secondary cooling specific water amount, is 0.2-0.3L/kg; finally producing bearing steel continuous casting square billets with the center porosity not more than 2.0 grade and the center shrinkage cavity not more than 1.5 grade, wherein the section size is 197-205 x 197-205 mm 2 。
(3) Rolling bars: loading the continuous casting square billet into a steel rolling heating furnace, controlling the highest temperature of furnace gas at 1200-1250 ℃ and the total heating time to be not less than 240min; discharging the continuous casting billet out of the furnace and then feeding the continuous casting billet into a roughing mill, wherein the rolling reduction of the first three roughing mills is respectively 37-45 mm, 53-61 mm and 75-83 mm; obtaining a finished product of the round steel after finish rolling, wherein the outlet speed of the finished product is 0.90-1.5 m/s, and the outlet speed is 62-70% of that of the conventional process; the specification of the round steel finished product is phi 70-90 mm, and the compression ratio, namely the ratio of the cross-sectional area of the billet to the cross-sectional area of the final round steel finished product is 6.29-10.40.
(4) The obtained round steel meets the standard requirement of high-quality steel of GB/T18254-2016 high-carbon chromium bearing steel through macrostructure detection.
Examples 1 to 5: the method for producing the large-size high-carbon chromium bearing steel bar with the small compression ratio adopts the following specific process.
(1) After converter primary smelting, LF refining and RH vacuum treatment in each example, molten steel of GCr15 steel was obtained.
(2) The process parameters of each example are shown in table 1; and continuously casting molten steel of the GCr15 steel and rolling the bar to obtain the bar-round steel.
Table 1: process parameters of the examples
In table 1, the rough rolling reduction is the reduction of the first three rough rolling mills, i.e. the difference in height between the original billet and the rolled piece after rolling.
(3) The round steel produced in the embodiments 1-5 is detected according to the standard requirement of GB/T18254-2016, the detection result meets the standard requirement of high-quality steel of high-carbon chromium bearing steel, and the result is shown in Table 2; typical photomicrographs of the round bars obtained in each example are shown in fig. 1-5.
Table 2: low power test result of the obtained round steel
As can be seen from figures 1-5 and table 2, the method realizes the rolling of large-specification bearing steel bars by continuously casting square billets at a small compression ratio, and the macrostructure meets the standard requirement of GB/T18254-2016 high-carbon chromium bearing steel quality steel. Therefore, the method expands the use limit of bearing steel blank production bars, improves the utilization rate of equipment, and solves the dilemma of enterprise production organization.
Claims (4)
1. The method for producing the large-specification high-carbon chromium bearing steel bar with the small compression ratio comprises the processes of continuous casting and bar rolling, and is characterized in that the continuous casting process comprises the following steps: protecting and pouring in the whole process, wherein the temperature of molten steel in the tundish is 1465-1485 ℃; the electromagnetic stirring current of the crystallizer is 330-350A, and the frequency is 3-4 Hz Hz; the current of the secondary cooling end electromagnetic stirring is 340-360A, and the frequency is 8-9 Hz; the withdrawal speed of the continuous casting billet is 0.8-1.0 m/min, and the secondary cooling solidification is carried out, wherein the secondary cooling strength is 0.2-0.3L/kg; the central porosity of the obtained continuous casting square billet is not more than 2.0 grade, the central shrinkage cavity is not more than 1.5 grade, and the section size is 197-205 multiplied by 197-205 mm 2 ；
The bar rolling process comprises the following steps: putting the continuous casting square billet into a steel rolling heating furnace for heating; after the continuous casting billet is discharged, the continuous casting billet enters a roughing mill, and the outlet speed of a finished product with the diameter of 70-90 mm of the round steel is 0.90-1.5 m/s; rolling into round steel with the diameter of 70-90 mm.
2. The method for producing the large-specification high-carbon chromium bearing steel bar material with the small compression ratio as claimed in claim 1, wherein the method comprises the following steps: in the process of rolling the bar, the highest temperature of furnace gas during heating is controlled to be 1200-1250 ℃, and the total heating time is not less than 240min.
3. The method for producing the large-specification high-carbon chromium bearing steel bar material with the small compression ratio as claimed in claim 1, wherein the method comprises the following steps: in the bar rolling process, the rolling reduction of the front three roughing mills is respectively 37-45 mm, 53-61 mm and 75-83 mm.
4. The method for producing large-specification high-carbon chromium bearing steel bars with a small compression ratio according to claim 1, 2 or 3, characterized in that: the high-carbon chromium bearing steel is GCr15.
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| CN202210854647.5A CN115401175A (en) | 2022-07-20 | 2022-07-20 | Method for producing large-size high-carbon chromium bearing steel bar with small compression ratio |
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